Reed College Canyon

Canyon Resources

An Exploration of some Chemical, Physical, and Biological Features of the Reed Canyon Reach of Crystal Springs Creek, Portland Oregon, in the Fall of 1994

Natural Science 110 class at Reed College, Fall 1994

Thomas G. Dunne*, Arthur Glasfeld*, Jimmy Huang, Randie Dalziel, Josh Filner, Steven Frantz and Students of the Fall Semester 1994 Natural Science 110 Class

Contribution from the Department of Chemistry, Reed College, Portland, Oregon 97202-8199

The following article was produced by students and faculty in the Natural Science 110 class at Reed College, Fall 1994. Copyright ©1994 Reed College

This article is being published as a historical reference. Some information may no longer be current.

Abstract: The unusual recent algal bloom in Reed Lake is found to probably not be primarily caused by unusually large values of nitrate or phosphate. Instead we propose for further study the hypothesis that the aquatic ecology of the canyon is being damaged by unusually low summer flow rates of water through the canyon. Several additional features of canyon water are reported in this attempt to initiate a chemical and physical data base for the waters of the Reed Canyon. In addition, coliform bacteria concentrations were found to exceed drinking water standard values by more than an order of magnitude.

* Authors to whom inquiries should be addressed.

Introduction

The Reed Canyon has received remarkably little scientific attention for an ecological system which is centered on the campus of a research intensive college. Those studies that have been done of this system were primarily biological[1, 2] except for the early work of Louise Odale[3]. Hence, this attempt to understand the chemical and physical causes and effects of the extensive and reputedly unprecedented canyon algal bloom of the summer of 1994 must be more of an exploration than a study designed for probable persuasive conclusions.

Experiments which we hoped would have the greatest relevance to this bloom problem were the measurement of nitrate and phosphate concentrations, since the availability these solution species are generally considered to limit the rate of aquatic plant growth. In addition, the measurement of dissolved oxygen (O₂) was carried out in order to determine whether the bloom had caused eutrophication in deep waters in the canyon.

Other experiments of assumed lesser probable relevance to explaining the bloom problem were carried out in this project to further characterize the waters of Reed Canyon and to fill the schedule for this one semester course laboratory. These were as follows:

1. Environmental Protection Agency Streamwalk investigations of eight one hundred foot segments of the flowing stream at the western extremity of the Reed Canyon.
2. Water depth and temperature measurements at semi-random points throughout Reed Lake.
3. Water flow rate measurements at three points in the Reed Canyon.
4. Measurement of water conductivity, conventional hardness and pH at two points in the Reed Canyon.
5. Coliform bacterial counts in three areas of the Reed Canyon.
6. Simulation of the acid rain leaching of base metals from sediments by measuring the loss of lanthanum from pulverized canyon sediments upon their soaking in waters of varying pH.

Experimental Section

All experiments were carried out in two hour laboratory periods by groups consisting of two to four students. In developing the procedures described below our goal was optimize the experience of such groups over these short periods with research quality data resulting from each group. We believe that in the case of most of these experiments we have come close to reaching this goal. However, most of these procedures will probably be at least slightly modified before their next use based on this first trial experience.

The determination of the concentration of nitrate ion was carried out on water samples collected at either the picnic area bridge (PAB) below the dam in the west canyon or the south upper canyon bridge on the path leading out of the canyon to SE 37th Street (SUB) by a modification of a method in the literature which is based on the nitration of salicylic acid followed by absorbance measurement of a solution containing the conjugate base of the nitrated product[4].The modified procedure is as follows: To a porcelain crucible add a 10.0 mL water sample and 2.0 mL of 0.031 M sodium salicylate; using a hot plate, carefully evaporate this solution just to dryness; set aside the crucible in a drierite filled dessicator for four weeks; add 2.0 mL of concentrated sulfuric acid to the crucible; after about ten minutes of gentle swirling of the crucible carefully transfer its contents to about 20 mL of nanopure water and then use additional water to assure quantitative transfer from the crucible; to this solution add 20 mL of an aqueous solution of NaOH and potassium sodium tartrate tetrahydrate (10M and 0.21M, respectively); now transfer this solution to a 100 mL volumetric flask and make up to volume; measure the absorbance of this solution at a wavelength of 420 nm on a spectrophotometer (a Bausch and Lomb Spectronic 20 instrument was used in our case). Apply the above procedure to solutions of known nitrate concentrations (KNO_{3 -} made up in nanopure water) and fit the date to the best equation obtained by using the linear least squares method.

Phosphate analysis was carried out by each laboratory group on the same water sample as that used for nitrate concentration determination. The method for the analysis of phosphate ion was a colorimetric procedure based on a spectrophotometric antimonyl- phosphomolybdate method in the literature[5]. The modified procedure is as follows: Four clean, acid washed test tubes (14 mm x 150 mm), each equipped with a stirring rod are placed in an open-bottom test tube rack situated on a fluorescent light box. To three of these tubes are added , respectively, 10.0 mL of standard solutions of different concentrations (in our case the standard concentrations were 0.05 mgP/L, 0.10 mgP/L and 0.15 mgP/L made up with nanopure water and KH₂PO₄). To the fourth tube is added 10.0 mL of a water sample of unknown phosphate concentration. Now the student team ( two to four members ) as simultaneously as possible with vigorous mixing adds to each of the four test tubes 1.6mL of combined reagent (Freshly prepared by adding sequentially to 50 mL 2.5 M H₂SO₄, 15 mL 0.00821 M potassium antimonyl tartrate ( K(SbO)C₄H₄O₆·0.5H₂O), then 15 mL 0.032 M (NH₄)₆Mo₇O₂₄·4H₂O. and then finally 30 mL 0.100 M ascorbic acid). After allowing about 15 minutes for color development, depth of color comparisons are made between the unknown and standard solutions to arrive at an estimated phosphate concentration for the unknown solution.

Dissolved O₂ concentrations at student selected sites in Reed Lake were measured from onboard three-person rubber rafts by a Yellow Springs Instruments (YSI) Model 50B dissolved oxygen meter equipped with a robust version of the Clark voltammetric oxygen sensor[6], the YSI 5739 Field Probe taped to a paint graduated (0.1m) copper tube pole of 1.5 m length. Measurements were made at depths of 0.2 m and 1.5 m (if possible). The instrument was calibrated in air just before each laboratory session. No altitude or air pressure corrections were made of the meter readings because of our low and constant altitude (about one hundred feet above sea level) and the fair weather experienced throughout the four week laboratory period (September 12, 1994 to October 7, 1994). At each site the water depth was measured with a simple device (designed and constructed by R. D.) consisting of a buret stand (38 cm x 16 cm base) with a long iron rod attached. The entire rod length was graduated in 0.1 m intervals with white paint. Water temperatures were also measured using the thermistor probe of the dissolved oxygen meter.

Water flow rates were measured at three locations in the Reed Canyon. Moving in a downstream direction these locations were as follows:

1. The exit culverts from the head pond. Since this location is on the private property of Dr. Andris Ritmanis we call this location Ritmanis Pond (RP).
2. The streams passing under the bridges on the trail leading out of the canyon to SE 37th Street (total flow rate). We label this location, UB (Upper Bridges).
3. The bridge at the picnic area in the lower canyon. We label this location, PAB (Picnic Area Bridge).

At location RP the flow rate was small enough to permit timing the flow from each of the two culverts there into one of two large buckets (volumes equal to 14 L and 18 L, respectively). At the other two locations the flows were measured by timing the passage of brightly painted corks over measured lengths of stream reaches. To obtain volume flow the stream depth and stream width were also determined as averages of many measurements of these dimensions along the reach.

Electrical conductivity, pH, and hardness were determined in the laboratory for water samples freshly collected at two different locations in the canyon (PAB or SUB).

Electrical conductivities were determined using a YSI Model 35 conductance meter equipped with a Model 3401 Immersion Cell (Cell constant, K = 1.0 cm^-1) The laboratory temperature averaged about 20°C. The pH was measured with Corning Model 320 pH meters calibrated at pH's = 4.00 and 7.00. Water hardness was determined by titrating 200 mL samples with 0.01000 M Na₂H₂EDTA·2H₂O using an Arsenazo indicator as described by Fritz and Schenck[7]. This entire literature procedure was scaled up by a factor of four. We found that the observation of the end-point was enhanced by doing the titration over an illuminated fluorescent light table.

Canyon waters from three different general locations were assayed for the presence of coliform bacteria using a membrane filtration technique[8]. Twenty five milliliters of the sample were diluted ten-fold with nanopure water and filtered through 0.45 micrometer pore size membrane (47 mm diameter). The membranes were then transferred to agar plates (1.5 % w/v) containing m Endo Broth (Difco) and incubated overnight at 37 °C. Green, metallic colored colonies were taken to be evidence of coliform bacteria, and the colony density per square cm was determined and the extended to calculate the total number of coliform bacteria per liter in a given sample of canyon water.

For each of six lab sections canyon sediment samples were grabbed in three polyethylene sandwich "baggies" from a location unique to the particular section. Three of the locations were under the three respective stream bridges on the path leading out of the canyon to SE 37th Street: SUB, Middle Upper Bridge (MUB) and North Upper Bridge (NUB). The fourth location was PAB. The fifth location was under the bridge just east of the theatre building (THEAB). The sixth location was about six feet west of the theatre stream overhang section (WETHEA). The contents of each set of "baggies" were transferred to a 75 mm x 150 mm glass petri dish. Excess water was decanted away. The dish placed in a drying oven set at 110°C and drying was allowed to proceed for one week. In order to remove large bodies from the dried sediment sample it was then strained through a sequence of two metal kitchen sieves. The first sieve had square holes of dimension 1.5 mm. The second sieve had rectangular holes of dimensions 1 mm x 0.5 mm. Several grams of sieved sediment were then distributed to each of the six (typical) student laboratory groups. The students then ground their samples to the consistency of powdered chocolate. Each powdered sample was then placed in a 21 mL glass vial so as to fill about one quarter of its volume. The vial was then filled with one of the following aqueous liquids: nanopure water, 0.10 M HNO₃ and 1.0 M HNO₃. Each of these liquids was used by two groups in a typical laboratory section. The vials were capped (plastic screw caps) and then placed in a partitioned cardboard vial box on top of an orbital shaker table and moderate shaking was commenced and continued for a period of days - the period varying from section to section. In order to enhance liquid - solid contact the vial position (top/bottom) was changed every few hours.

After the above soaking was complete the samples were prepared for neutron activation in the 250 kW TRIGA nuclear reactor as follows:

1. The solid was removed from the soaking liquid by vacuum filtration.
2. Except for one case the filtrate was discarded and only the solid was retained.
3. The solid was washed on the filter with nanopure water.
4. The solid was oven dried and a small portion of the dry sample is placed in a vial and its mass was determined.

Results

Nitrate and Phosphate Concentrations. Standard solutions of four different nitrate nitrogen concentrations in the range expected for canyon water were found after our chemical procedure to have absorbances of light at a wavelength of 420 nm shown in Table 1.

Table 1. KNO₃ Nitrogen Concentration and Absorbance at 420 nm

The Table 1 data was fitted to a best straight line by a linear least squares analysis with the following equation resulting:

A = ( 0.0826 +/- 0.0014 ) x C_N - ( 0.0047 +/- 0.0065 ) ( 1 ).

Note: The Beer - Lambert Law is obeyed within experimental uncertainty. To calculate the canyon water concentrations the solution of Equation ( 1 ) was used:

C_N = ( A + ( 0.0047 +/- 0.0065 ) )/( 0.0826 +/- 0.0014 ) ( 2 )

The nitrate nitrogen and phosphate phosphorus ( C_P ) concentrations are shown in Table 2. The data shown are averages and the listed uncertainties are standard deviations of the results of thirteen laboratory groups except for C_N at PAB, where it was decided to use data from only twelve of thirteen laboratory groups, because the C_N from one group deviated from the average value by several standard deviations.

Table 2. Average Nitrate and Phosphate Concentrations

in Canyon Water October 10 to October 14, 1994

Dissolved Oxygen Concentrations and Temperatures of Canyon Water (Reed Lake). The average dissolved oxygen concentration at two water depths (0.2 m and 1.5 m) as percentages of the air saturated oxygen concentrations at the temperature of measurement (%(O₂Sat.)Avg.), and the average temperature (t(°C)Avg.) are reported in Table 3.

Table 3. Average Dissolved Oxygen Concentrations and Temperatures

in Canyon Water September 12 to October 7, 1994

We attempted to locate our lake sites by latitude and longitude measurements using the Global Positioning Satellite System. This attempt failed apparently because the Department of Defense was "fuzzing" this system at the time of our measurements. All that we can now say about site positions is that they are somewhat random about the lake and the deeper sites (depth > 1.4 m) were in the western region of Reed Lake.

Streamwalk. The eight one hundred foot study segments of the western campus reach of Crystal Springs Creek were studied following the simple protocol described in EPA Streamwalk Manual (EPA 910/9-92-004) by thirty six laboratory groups. Most of these groups studied a single segment, but two groups studied multiple segments, so the total study redundancy for a typical segment is about five. The reported latitudes and longitudes obtained by use of a U. S. Geological Survey map ( Lake Oswego Quadrangle ) were corrected, if need be, and the entire bundle of thirty six reports was transmitted to the EPA via Ivy Frances of the City of Portland, Environmental Services Department. Frances expressed particular interest in our Streamwalk investigation, because its significant redundancy might permit a test of the reproducibility of Streamwalk data. To date (5/24/95) we have received no indication from the EPA that such a reproducibility test has been made using our data. The most memorable observation from this study was the large width and barren banks of the stream reach that flows under the theatre building overhang.

Depth, Area and Volume of Reed Lake. A total of thirty eight water depth measurements in Reed Lake were made simultaneously with the dissolved oxygen concentration and temperature measurements.

The resulting average depth is (1.3 +/- 1.0) m. The range of measured depths was 0.28 to 3.7 m. The former value is undoubtedly for a site close to the eastern end of Reed Lake and the latter value is undoubtedly for a site close to the western end of Reed Lake.

The area of Reed Lake was estimated by using a remarkable small scale ( 1 in.: 200 ft. ) map of the Reed neighborhood produced on September 24, 1992 by VESTRA Resources. A 1:1 xerox copy of an area of this map containing Reed Lake was made. A fine scissors was then carefully used to cut the Reed Lake segment from this copy. This segment was then weighed on an analytical balance as was a square segment of known map area (9.00 (in)²) cut from the same copy. The weight : area proportionality was then used to calculate the map area of this Reed Lake ("dragon-shaped") segment. Finally the scale of the map was used to scale up to an area for Reed Lake. This was found to be equal to 1.51 X 10⁵ (ft.)².

The volume of the Reed Lake can now be roughly estimated to be equal to 6 X 10⁵ (ft.)³ using the previously acquired average depth of Reed Lake.

Water Flow Rates in Reed Canyon.

Table 4. Average Dry Weather Flow Rate Data at Three Sites in the Reed Canyon

A rough estimate of the average residence times for water in Reed Lake can be obtained by dividing the PAB flow rates into the above estimated volume of Reed Lake. For the period 9/12/94 to 10/7/94 the estimated average residence time is about one day. For the day 7/7/94 the estimated residence time is about four days.

Water Electrical Conductivity, Hardness and pH.

In Table 5, below, average laboratory electrical conductivity, hardness, (as (mg CaCO₃ equivalent)/L), and pH are reported for water samples freshly (usually) collected at two locations, PAB and SUB during the period October 24, 1994 to October 28, 1994. This is an interesting period, because during it the dry spell of weather that we had experienced during the first half of the semester was broken with a record (for Portland) twenty four hour rainfall. For that reason weather service rainfall depths recorded by the U. S. Weather Bureau at Portland International Airport for the twenty four hour period beginning at midnight prior to the sample collection date are also reported in this table.

Table 5. Collection Date, Rainfall Depth on Collection Date (RFD - 1/100's in.), Average Electrical Conductivity (Cy - micromhos/cm), Hardness (H_d - (mg CaCO₃ equivalent )/L) and pH for Canyon Water Collected at Two Locations.

Where more than one laboratory section analyzed portions of a given water sample the results of these sections are reported on a separate line with the later date of analysis given after a dash mark.

*P is designated here to distinguish an afternoon laboratory section on this day from its morning section. The data from the morning section has been neglected because it is both sparse and for water samples of questionable origin.

Coliform Bacteria Concentrations. During the period from October 31, 1994 to November 4, 1994 water samples were collected at various locations in the canyon and the coliform bacteria concentrations in these samples was determined. Table 6 displays a subset of this data chosen because the samples for this subset were either subjected to multiple analyses (10/31 and 11/1) or multiple samples collected in the same laboratory period were acquired at approximately the same site in the canyon.(11/3). Since the samples were collected during a week of variable rainfall the type of rainfall data reported in Table 5 is also reported here. Two of the three sample sites are as designated above (SUB and PAB). The third site, PORT, is located on the south bank of Reed Lake about thirty six trail yards east of the main canyon bridge. It is so designated because this site was also the port of embarcation for the rafts used for the in situ canyon experiment.

Table 6. Average coliform bacteria concentrations ( Conc. - L^-1 ).

Simulation of an Anticipated Effect of Acid Rain the Leaching of Base Metals from Sediments by Acidified Water. In general the experimental results were not in persuasive agreement with the hypothesis that greater base metal ( lanthanum in our case ) loss from the sediment should occur as an increasing function of decreasing pH of the soaking liquid. In order to give some idea of the current status of this experiment we report one typical data set in Table 7. The soaking time for these sediment samples was 90 hours. The samples were prepared by the six groups of the Thursday afternoon laboratory section (Sample Site: THEAB).

Table 7. The reported pH's are those, respectively, estimated for CO₂ saturated nanopure water, 0.10 M HNO₃ and 1.0 M HNO_3. Sample Mass (S. M. - grams). Time period from reactor irradiation termination to the time of gamma ray counting (t - days). Raw Count for a 15 minute period (R.C.). Count corrected back to the time of irradiation termination per gram of sediment (C.C./ S.M. - g^-1).

Discussion

The first issue to be addressed is whether the extensive algal bloom in Reed Lake in the summer of 1994 was primarily the result of unusual concentrations of the plant nutrient ions nitrate and phosphate. The concentration data base for these ions in Reed Lake is nearly empty in that there is but a single value, that measured for nitrate by Louise Odale[3]. Her single value for the nitrate nitrogen concentration in Reed Lake on February 25, 1932 was 0.06 ppm or 0.06 mgN/L. How can we explain the two orders of magnitude difference between her value and our values? Three general explanations of this large discrepancy seem to be most probable: 1) In the past 62 years the nitrate pollution of Reed Lake has grossly increased. 2) Our methodology is incorrect. 3) Odale's methodology is incorrect. The first possibility seems unlikely, since our nitrate concentrations are not excessive by modern standards (e.g. The current EPA drinking water standard for nitrate is that its concentration be less than 10 mgN/L). Also, Reed College in 1932 was hardly set in a pristine environment. Even then the Reed neighborhood was an urban one and the Reed campus was only a couple of decades away from being Mr. Ladd's cow pasture. The second possibility also seems unlikely, since our nitrate concentrations are in quite good agreement with recent nitrate concentration measurements taken by the U. S. Geological Survey on Crystal Springs Creek about two miles downstream from the Reed College campus just above the confluence with Johnson Creek[12]. The Survey value measured there on October 3, 1989 was 5.46 mgN/L, which is bracketed by our two values. Also of interest from the Survey study are the values for other nitrogen containing solute species on that same date: 1) Total organic nitrogen, 0.14 mgN/L. 2) Ammonia, 0.08 mgN/L. 3) Nitrite ion, 0.04 mgN/L. From the relatively small magnitudes of these other concentrations we feel justified in just using the nitrate concentration to get an approximate measure of the available compound nitrogen containing plant nutrient in our reach of Crystal Springs Creek. Odale's average value for ammonia in Reed Lake (winter of 1932) was 0.040 mgN/L, within a factor of two of the 1989 Survey value for this nutrient species. The Survey has also recently drilled a test well in nearby Kenilworth Park. Water from this test well collected at a depth of 109.5 +/- 2.5 ft. on July 18, 1995 was found to have a nitrate nitrogen concentration, C_N = 5.76 mgN/L[13], insignificantly different from our above average SUB site average value. This close agreement of independently measured nitrate nitrogen concentrations at two closely spaced times and sites lends additional support to the quality of our data. Finally, we must tentatively conclude that the algal bloom of 1994 did not have excessive amounts of nitrate ion as its primary cause, since the Survey Crystal Springs Creek values throughout the presumably normal algal growth year of 1989 were in our measured range for nitrate. Similarly, our measured values for phosphate phosphorus concentration shown in Table 2 are probably not significantly different from the Survey value for October 3, 1989, 0.10 mgP/L. It therefore seems unlikely that excessive concentrations of phosphate are the primary cause of the recent algal bloom. Clearly it would be good to know how Reed Lake nutrient ion concentrations compare with those at the Survey site taken on the same date. We plan to make the measurements supporting this comparison in the near future. Attempts are also being made to contact Louise Odale to see if her memory or her laboratory notes might shed some light on her low nitrate concentration values.

The drop in both nitrate and phosphate average concentration values (seen in Table 2) on going from the east canyon SUB site to the west canyon PAB site is of interest, even though the phosphate concentration drop may not be significant. We speculate that this drop may be the result of stratification of concentrations in the Portland Terraces aquifer. The higher elevation of the SUB site may yield water that is more polluted because of better chemical communication of the strata feeding the east canyon springs with the highly developed area of the Reed College neighborhood. On the other hand, the lower elevation of the PAB site would lead the water there to originate from a greater variety of aquifer depths, the deepest of which may be less polluted. This concentration drop observation demands further study with a more precise phosphate methodology and over a yearly seasonal cycle to isolate possible biological causes.

Caution must be used by anyone making use of our rough estimate of the volume of Reed Lake, since no special effort was made to randomize the sites of our depth measurements. In the future an effort will be made to uniformly cover Reed Lake with depth measurements so that a more realistic average depth can be acquired yielding a more reliable lake volume. For the present it is probably best to just make the memorable order of magnitude statement that the volume of Reed Lake is about a million cubic feet. The lake volume is an important piece of data to measure periodically, in addition to its use for estimating water residence times, because it will allow the quantitative monitoring of the degree of siltation that concern numerous observers of Reed Lake[14].

The most notable feature of the water flow rate data displayed in Table 4 is the almost two orders of magnitude increase in flow rate on going from the far east canyon RP site to the west canyon PAB site observed for the period 9/12/94 to 10/7/94. Clearly the observers of the canyon of long-standing are correct in saying that the Reed Canyon is fed by multiple springs arrayed along the length of the canyon[15]. Indeed, Crystal Springs Creek is well named, because if one proceeds downstream to its terminus at its confluence with Johnson Creek one finds even greater rates of dry weather flow. For instance, George Sexton and T. G. D. measured a dry weather flow rate of ( 16 +/_ 3 ) ft.³/s at that site on August 8, 1994, a value roughly a factor of two greater than the our highest value measured in the west canyon. Our measured value at the confluence site is not significantly different than the value of 13.0 ft.³/s reported at that site in August 1989 by the Survey[13]. The apparent significant increase in flow rate at the PAB site on going from a mid-summer day to an early fall period seen in Table 4 is of interest, since it can neither be attributed to intervening rainfall (there was none) or to irrigation pumping by Reed College (the pumps were off for all measurements). Although we need to verify this apparent seasonal flow variation and will try do so at more than one site in 1995, we still can not resist the speculation that the extreme algal bloom in the canyon last summer may have been the result of unusually low summer water flow rates. This low flow, perhaps the result of enhanced pumping of the aquifer through newly dug wells, could, as Heather Helming[16] has suggested, result in unusually warm water, which, in turn, might support unusually rapid aquatic plant growth. We plan to test the response of canyon vegetation to temperature variation in the laboratory in during the summer of 1995. Preliminary work by Tommy Richter and T.G.D. on a summer day profile of water temperatures in the canyon support the idea that low summer flow rates may cause thermal equilibration with the ambient atmosphere. In this brief study in the middle of the afternoon on August 11, 1994 we found that at the east canyon SUB site the water temperature was 14.8 °C, at the mid- canyon PORT site, 18.3 °C and at the west canyon dam culvert site, 20.0 °C, close to the ambient air temperature, 21.8°C. It should be mentioned that under the low summer flow conditions in the canyon the impact of Reed's own irrigation pumping may not be negligible. The capacity of Reed's pumps total 0.5 ft.³/s [17], about 25% of our estimated mid-summer flow rate for 1994. Finally we must explain why the potentially relatively precise "bucket method" used at site, RP, yielded an average flow rate value with a variance just as high as those for the the UB and PAB sites. Beavers busily plugged the Ritmanis Pond culverts prior to each laboratory meeting despite our efforts to clean these culverts on the morning of each laboratory day. In future flow studies at this site we hope to let the beavers do their plugging work and then have each laboratory group freshly unplug the culverts just prior to measurements of flow rates. The group will then make several measurements until the flow rates drop to a steady value - a nice demonstration of the approach of the steady state, we hope. It has been wisely suggested that keeping track of the declining hydrostatic head as the steady state is approached would add physical meaning to these measurements[18], so we plan to add that feature to this now beaver assisted experiment.

The data in Table 5 are consistent with what is known about Crystal Springs Creek and is semi-quantitatively self-consistent. For instance, our dry weather hardness values are not significantly different from the dry weather value of 83 mg CaCO₃/L measured at the confluence by the Survey on October 3, 1989[12]. Self consistency comes from the expectation that HCO₃^- will be the predominant species in a water sample soaked by aerial CO₂ and heavily mineralized by dissolved CaCO₃ and MgCO_3. For such water, pH's in the range somewhat above seven are to be expected. Modelling the electrical conductivity of such a solution using literature values for the specific conductivities of the major ions, Ca²⁺, ^Mg2+ and HCO₃^-,[19] accounts for the most of the measured electrical conductivity. The record rainfall of 4.77 inches in less than two days reduced both hardness and the electrical conductivity of Reed Lake water by about 40%. Converted to meters this rainfall depth is 0.12 m or only about 10% of the average depth of Reed Lake giving an expected concentration reduction by dilution of 10%, only 25% of the observed value. We believe that this discrepancy is the result of additional rainwater entering the lake as campus run-off and the incomplete mixing of rainwater with the deeper lake waters. We are not prepared to say which of these factors is the more important one. As expected, the SUB site, upstream from Reed Lake has hardness and concentration higher than that for the PAB site one day after the heavy rain, because the entire Reed Lake volume acts to buffer the recovery of concentrations at the latter site. The hardness of Canyon water is good news for aquatic creatures, since the toxicity of a variety of dissolved metal ions tends to go down appreciably as the water hardness goes up[20].

^{At all sites and at all times the coliform bacteria concentrations of Reed Canyon waters ( Table 6 ) were found to greatly exceed the current least stringent drinking water standard, 100 L}-1 (World Health Organization - 1984). The much higher coliform concentration during a heavy rainfall is likely the result of run-off from soil, which typically has a higher bacterial content than most natural waters[21]. Our data does not support the original hypothesis of this experiment that coliform concentrations should be higher for water that has flowed through Reed Lake with its considerable duck population.

^{The typical data shown in Table 7 does not clearly support the hypothesis that acidified natural waters will extract base metal ions like La}3+ in that the variance in C.C./S.M. for water of a given pH is of the same magnitude as that for waters of different pH's. The question of this experiment is still an important one to deal with here soon, because the great plume of acid exhaust gases from Asia is on its way to the northwest coast of the United States. David Covert recently mentioned that this plume has currently covered about half the distance between coal burning Asia and here[22]. Evidence for a similar intercontinental transfer ( North America to Europe ) of acidic exhaust species, like SO_x and NO_x, has recently been stated[23]. We therefore feel that it is important to continue this experiment using local sediments with the following several improvements:

1. ^{The sediments should be microscopically characterized as to their general geochemical category.}
2. ^{The series of water soaking experiments (like the series in Table 7) should use sediment samples of the same well defined particle size.}
3. ^{To ensure more effective soaking, smaller and better defined amounts of sediment should be used for the water filled 21 mL soaking vial.}
4. ^{Soaking times should be varied. In particular, longer soaking times than the less than four day times of this experiment should be used.}
5. ^{Additional attempts should be made to analyze for the base metal ions extracted into the soaking liquid as well as the analysis of base metal ion loss from the sediment, because the former may turn out to be a more sensitive test of base metal ion loss.}
6. ^{Attempts should be made to analyze for base metals other than lanthanum.}

^{Acknowledgements}

^{We thank Helen Stafford, Bert Brehm, David Dalton, Bob Kaplan, Sally Schott, and Ellen Weider of the Reed College Biology Department for advice and help. We are grateful to Dr. Andris Ritmanis for making his pond available for our studies and for sharing his historical perspective of the upper Canyon. We also thank Ivy Francis and Eric Machorro of the Environmental Services Division, City of Portland, for access to information, help and advice. Marsh Cronyn of the Reed College Chemistry Department must also be thanked for sharing his almost sixty year view of Reed Canyon based activities. Ron McClard of the Reed College Chemistry Department and Scott Arighi are thanked for boating advice. We are indebted to Steven Ullrich for advice on water analysis. We are similarly indebted to Jim Cook City of Portland water laboratory. George Sexton and Tommy Richter are deserving of credit for invaluable experimental assistance. Useful information was obtained about the current chemical status of the Portland Terraces aquifer from Martell Kiefer and Steve Hinkle of the Portland office of the U. S. Geological Survey. Information from David Covert of the University of Washington and Krista Reininga of Woodward Johnson Associates is gratefully acknowledged. We also acknowledge the very good editorial assistance of Eve Lyons. Last, but surely not least, we acknowledge the excellent help of our teaching assistants: Ingrid Loma, Meredith Miller, Bruce Moreira, Elaine Shin, Chantal Sudbrack and K. J. Wood.}

^{Literature Cited}

^{[1]Cray, Caitlin. An Investigation of Aquatic Water Quality in the Canyon Through Use of Bioassay; Reed College Thesis, 1987.}

^{[2]Haws, Maria. Urban Stream Ecology: 3 Portland Streams; Reed College Thesis, 1985}

^{[3]Odale, Louise. Nitrogen Cycle in Water; Reed College Thesis, 1932.}

^{[4]Rump, H. H. and Krist H. Laboratory Manual for the Examination of Water Waste Water and Soil, 2nd ed.; VCH: New York, 1992; p116.}

^{[5]Official Methods of Analysis, 14th ed.; Association of Official Analytical Chemists, Inc: Arlington, VA,1984; p 632.}

^{[6]Skoog, D. A. and Leary, J. J. Principles of Instrumental Analysis, 4th ed.; Saunders College Publishing: New York, 1992; p 546.}

^{[7]Fritz, J. S. and Schenk, G. H., Jr. Quantitative Analytical Chemistry, 2nd ed.: Allyn and Bacon: Boston, 1969; p542.}

^{[8]Hach Water Analysis Handbook; Hach Company: Loveland CO; p 256}

^{[9]Blank, L. W.; Roberts, T. M.; Skeffington, R. A. Nature 1988, 336, 27.}

^{[10]Havas, M.; Hutchinson T. C. Nature 1983, 301, 23.}

^{[11]Huheey, J. E. Inorganic Chemistry, 3rd ed.; Harper and Row, Publishers: New York, 1983, p 74.}

^{[12]Edwards, T. K. Water Quality and Flow Data for the Johnson Creek Basin, Oregon, April 1988 to January 1990, U.S. Geological Survey Open File Report 92-73, Portland, Oregon, 1992.}

^{[13]Hinkle, Steven, U. S. Geological Survey. Private Communication.}

^{[14]Stafford, H. Private Communication.}

^{[15]Cronyn, M. Private Communication}

^{[16]Helming, H. Private Communication.}

^{[17]Hefner, B. Private Communication.}

^{[18]Covert, D. Private Communication.}

^{[19]Lide, D.R. (Editor-in Chief ), CRC Handbook of Chemistry and Physics, 75th ed.; CRC Press: Boca Raton, FL, 1994; p 5-90.}

^{[20]Oregon Administrative Rules , Private Communication, Kriste Reininga.}

^{[21]Machorro, E. Private Communication.}

^{[22]Covert, E. Private Communication.}

^{[23]Freemantle, M. Chemical and Engineering News, May 1, 1995; p 10.}